The management of sulfur continues to be a persistent problem for sour gas and natural gas operations. In many sour gas operations, elemental sulfur vapor in the gas can condense and deposit at various locations along the sour gas system causing numerous problems. For example, sulfur depositions in gas pipelines and processing facilities can increase the rate of corrosion in the pipes and cause leaks or blockages that interrupt normal operation of the gas lines. Subsequent removal and disposal of the sulfur deposits can then cause safety and environmental concerns. Due to the problems associated with removing sulfur deposits, there is a need for ways to accurately predict the location of future sulfur deposits within the structures of a gas line (e.g., pipeline, pressure vessels, etc.) and also to predict the maximum amount of sulfur that can deposit.
Oil and gas production technical professionals are generally well aware of the fact that elemental sulfur is often found, either saturated or at significant levels, in reservoir gases. They are also generally aware of the fact that pressure or temperature reduction of the gas can result in precipitation and deposition of sulfur from the gas. Alternatively, what is very difficult for them to know are the locations in their facilities where they might expect to find deposited sulfur and at those locations, how much sulfur might be expected to deposit. Because of this lack of knowledge, oil and gas production engineers have a difficulty determining how to manage potential sulfur deposition in their facilities and the subsequent problems it can create. What is needed, and what is lacking in current art, is a sulfur deposition prediction model developed for use by oil and gas production personnel. To create such a model, tailored for oilfield gas operations, three types of data are required:                1. The amount of sulfur dissolved in a gas where it enters gas handling facilities, which is a function of its composition, pressure, and temperature        2. The amount of sulfur dissolved in the gas as a function of temperature reduction        3. The amount of sulfur dissolved in the gas as a function of pressure reduction        
Using current art, it is difficult to determine the quantity of sulfur in a gas stream where it enters a gas facility. However, it is not cost-effective or particularly feasible with current art, to determine the amount of sulfur dissolved in the gas as a function of temperature or pressure reduction. The following paragraphs explain this in detail.
More specifically, in the current art, there are laboratory-based techniques available, which attempt to provide the means for the accurate determination of sulfur in a gas. All of the current art laboratory-based techniques utilize a closed system in which a volume of gas is pressurized to a required pressure inside of a fixed volume equilibrium cell or autoclave that is controlled at a required temperature. Although fully capable of simulating any oilfield gaseous environment, a closed system of fixed volume is incapable of providing the means for the accurate determination of sulfur in the gas. The deficiency with the current art, laboratory-based techniques, results directly from the closed system of fixed volume. An example and discussion will clarify this point.
For this example, it will be assumed that researchers seek to create a sulfur deposition prediction model for a 100% methane gas stream found in typical oil and gas production environments. Therefore, accurate determinations of elemental sulfur in methane gas at pressures and temperatures typically found in gas production facilities will be required to create the model. One set of conditions, typical in gas production facilities containing methane, is one in which the methane is at 300-psia pressure and at 45° C. temperature. To conduct their testing, the research staff will use a typical current art, closed, fixed volume, autoclave vessel. To their benefit, the research staff recognizes that the larger the volume of their vessel the more improved will be their test results. They therefore decide to use a very large fixed volume vessel of 10-liters volume. Under the conditions of 300-psia pressure and 45° C. temperature, methane gas could typically contain 0.01-pounds of elemental sulfur per million standard cubic feet of gas. Current art analytical chemistry techniques require a minimum of approximately 0.1-milligram of deposited elemental sulfur for accurate and precise determinations. Therefore, under these conditions of pressure and temperature, the volume of methane gas required to collect 0.1-milligram of elemental sulfur, would be approximately 625 liters at standard 1-atmosphere pressure. At 300-psia pressure, this is approximately 31 liters of gas. Considering that the test vessel is 10-liters in volume, it is readily apparent that it will be impossible to remove 31 liters of gas from a 10-liter vessel in order to meet the requirements of the analytical technique. This makes it impossible for the research staff in this example to develop a sulfur deposition prediction model for methane gas found in typical oil and gas production environments. It could be argued that a larger autoclave vessel could have been used. This might be true, but the cost and complexity of using larger pressure vessels increases at a staggering rate. However, there is another subtle point that will show the deficiency of current laboratory art. To determine, accurately and precisely, the amount of sulfur in a gas, a sufficient volume of the gas must be sampled in order to collect adequate sulfur for the analytical chemistry analysis. In the above example, this was approximately 31 liters. Regardless whether the volume of sampled gas is one milliliter or 31 liters, it does represent the physical removal of gas from the fixed volume vessel. If one milliliter of gas is removed from a fixed volume vessel, then there will be less gas occupying the same volume and the pressure inside of the vessel must decrease. It is established that the saturation level of elemental sulfur contained in a gas is directly proportional to the pressure of the gas. Therefore, as gas is removed from a current art fixed volume vessel, the pressure inside the vessel will drop, and so will the amount of sulfur contained in the gas. This problem cannot be overcome by current art laboratory-based fixed volume vessels.
It will be appreciated that the foregoing example is exemplary in nature and is presented for illustrating the deficiencies of conventional techniques.
Also in the art, there are field-capable techniques available to oil and gas production engineers, which feasibly can provide the means for the accurate determination of sulfur in a gas. In this situation of field-based testing, potentially accurate results can be obtained because of the large volume of gas normally available, which overcomes the limitation of lab-based measurements described above. However, these methods are not commonly used because by itself, knowing the amount of sulfur in a gas at one particular location provides the engineer with very limited knowledge. The engineer would not know the amount of sulfur in the gas upstream from the measurement location and would have no ability to predict if, or how much, sulfur might precipitate and deposit in facilities downstream from the measurement location. In theory, engineering staff could determine the amount of sulfur in the gas stream at multiple locations of varying pressure and temperature with a goal to create their own sulfur deposition prediction model. However, the cost, time, safety issues, and complexity of doing so would be cumbersome to the point of complete impracticability.
In summary, what is needed, and what is lacking in current art, is a sulfur deposition prediction model developed for use by oil and gas production personnel. To create such a model, tailored for oilfield gas operations, three types of data are required:                1. The amount of sulfur dissolved in a gas where it enters gas handling facilities, which is a function of its composition, pressure, and temperature;        2. The amount of sulfur dissolved in the gas as a function of temperature reduction; and        3. The amount of sulfur dissolved in the gas as a function of pressure reduction.        
It is the expressed intention of the present invention, by means of continuous gas flow capabilities, to generate, with accuracy and precision, these three data, which will provide the means for creating a sulfur deposition prediction model developed for use by oil and gas production personnel.